At present, in order to obtain sufficient three-dimensional information, a multiline Lidar having a large vertical field of view is usually used. A large area scan can be achieved by rotating Lidar and thereby rotating the vertical field of view with the Lidar. The angular distribution of beams in an existing multiline Lidar device is uniform within a particular angle range (that is, the angular distribution of laser beams in the vertical field of view is constant, and the vertical angular resolution is thus constant). For example, the vertical angular resolutions of 16-line, 32-line, and 64-line Lidars are respectively 2°, 1.33°, and 0.43°. For another example, the vertical angular resolutions of 4-line and 8-line Lidars are each 0.8°.
The constant vertical angular resolution can cause significant performance issues for the Lidar. For example, in some applications, a Lidar may be mounted on a vehicle to detect pedestrians, other vehicles, and the like on the ground. Assuming that the laser beams diverge from the Lidar in vertical planes, laser beams emitted upwards are mostly wasted because the main detection targets for Lidar are more likely to be on the same elevation level as the Lidar-mounted vehicle, and are substantially covered by horizontally emitted laser beams, making some non-horizontal beams like the upward beams excessive. By the same reason, insufficient horizontal beams incident on the main detection targets can result in low accuracies for their detections.
In addition, if the angular distribution of laser beams remains constant in the vertical field of view according to existing Lidar technologies, more laser lines are needed to achieve a higher vertical resolution, which results in a higher cost, a larger Lidar size, and a lower reliability and stability. Limited by the data capacity of Ethernet and the processing speed of in-vehicle CPU, a Lidar with more lines cannot achieve both high horizontal angular resolution and high scanning frequency.
However, if the number of lines are reduced to lower the cost while keeping the angular distribution of laser beams constant, the angular interval between laser beams becomes excessively large, and a target may not be recognized within a reasonable detection range (e.g., 40 meters away). For example, if the total vertical field of view is 32° and the interval (the vertical resolution) is 2°, 16 lines are needed, and then the intervals among laser beams 40 meters away are approximately 1.4 m. Due to the large interval of 1.4 m, a pedestrian at that position may be undetected.